Hi -
1. You need to configure the BIOS to boot from USB hard drive or USB stick (this is often a non-default option; the specifics will depend on your motherboard
2. Your USB media must be bootable (i.e. it must have a valid boot sector)
Strong suggestions:
1. New CD/DVD drives aren't that expensive - consider buying one
2. There are also USB CD/DVD drives: this might be ideal for you
3. Alternatively, you can boot Linux from a USB stick. For example:
http://www.debuntu.org/how-to-instal...nux-on-usb-bar
4. Finally, maybe you can install and run RedHat (or CentOS, which is pretty much the Same Thing ;-)) on a VM running on whatever operating system is currently installed on your desktop:
http://www.thoughtpolice.co.uk/
'Hope that helps .. PSM